In replying to an earlier post, I mentioned that I too was looking for a way to stop lichen growing on my close-board and palisade fences. In Autumn 2017 (before the lichen growing season), I sprayed a number of close-board fence panels with 2% benzalkonium chloride but left a couple untouched as controls. As of today the results are most satisfactory: virtually no lichen on the treated panels and lots of lime-green stain on the controls. Next step will be in November this year when I will spray the same solution on 60 metres of palisade fence as soon as the hawthorn hedge immediately behind it has shed its foliage.Until now I have been treating all my fences in late February with Cuprinol Ducksback (brushed on to palisade fence stakes) or the sprayable version (sprayed on to fence panels). Mistake; the problem with this is that it is painting over the lichen, and the result is a rougher and rougher texture - and lichen loves a bit of rough!

One warning to anyone else using this stuff, even when dilute: use wrap-around safety glasses or even swimming goggles. It is notoriously bad on the eyes.

Put a strip of lead along the top of the fence. Lasts longer, doesn't get in your eyes. If in doubt look at an old roof below the flashing areas (provided they have paid for proper lead flashing) - dspp

What's wrong with lichen anyway? One of the earth's oldest botanical forms, and a sure sign that your air's clean. Around these parts, we spray dilute cow dung and live yoghurt onto stonework just to encourage its growth. (And to help bright new stonework to age in quickly)

Okay, you can get it off stonework with anti-algal solutions - or with (very dilute) bleach, if you're really, really careful. Personally, I try not to use lead because of the way it leaches into the ground - copper strip will do a similar job, and is readily available (as a slug repellent). Not sure what your options are on wood, though, especially if it's encrusted under paint where it'll burst forth whenever it wants to. I fear you're going to have to scuff it up before you can treat it, but on 60 metres of palisade that's going to take a while.....

Around these parts, we spray dilute cow dung and live yoghurt onto stonework just to encourage its growth

In my village, live yoghurt - in fact any yoghurt whether sprayed or drunk would be regarded as an affectation and an effete middle-class habit.Cow dung on the other hand is everywhere to the extent that evolution has probably created a local cow-dung-symbiotic lichen.

I am not anti-lichen - I have lichen on my house walls and a shag-pile carpet of moss on my roofs (very rough double-roman tiles), just anti-lichen when it won't do what it is told.